Motor-control switch



Patented Dec. 9, 193';

UNITED STATES PATENT OFFICE B. EDSALL, OI BROOKLINE, MASSACHUSETTS, ASSIGNOB TO CONDIT ELEC- TRICAL MANUFACTURING CORPORATION, OF SOUTH BOSTON, MASSACHUSETTS, A

CORPORATION 01 MASSACHUSETTS MOTOR-CONTROL SWITCE Application filed Kay 29,

This invention relates to small electric switches of the air break type especially adapted to control small electric motors.

A motor starting and controlling switch of the class with which this invention is particularly concerned must be small and compact so that it can be located in any convenient place in a factory. One type or size of switch should be able to control various sizes of motors the horsepower ratings of which vary between rather wide limits or from fractional ratings up to, say, ten or fifteen horsepower. By reason of the small dimensions which the requirement of com actness imposes upon the switch, it has been ound to be rather diflicult to design a small switch which will operate satisfactorily with the larger sizes of motors, the main difiiculty involved being the magn tude of the circuit interrupting are that is formed between the contact members of the switch when the switch closes on starting current or opens under heavy loads on theIarger motors and the difiiculty of extinguishing the arc in a restricted space and within the short length of separation of the contact members.

It is an object of the present inventlon to provide a switch of the type described with means whereby the magmtude of the circuit interrupting arc is kept down within reasonably small limits and the arc is rapidly extinguished.

A further object of the invention is the provision of an electric switch of the type set forth with means which provides two circuit interrupting arcs in series and means to provide a resistance across one of the circuit interrupting arcs and in series with the other are whereby to limit the magnitude and efiect the rapid extinguishment of the arcs.

A further object of the invention is generally to improve the construction and operation of electric switches of the type above set forth.

Fig. 1 is a front elevation of a three-phase air-break electrically-operated electric switch embodying the invention.

Fig. 2 is a sectional elevation taken along line 2-2 of Fig. 1.

Fig. 3 is a single phase diagram of the cir- 1928. Serial No. 281,425.

cuit connections through the switch and the arc-shunting resistor therefor.

The switch .here shown is enclosed within a metal casing having the two separable parts 10 and 12,'the part 12 comprising a removable cover for the casing. An insulating supporting plate 14 is located within the casing and is fixed to the part 10 thereof. The switch operating mechanism includes a U-shaped electro-magnet 16 mounted on the lower part of the supporting plate 14 and having an actuating winding or coil 18 which is adapted to be maintained normally energized to hold the switch closed. A pivotally supported armature 20 is operated by said electro-magnet and comprises the support for the movable switch members.

A plate 22 is fixed to said armature and has arms 24 at its upper end to and between which an insulating bar 26 is secured. Said bar constitutes an insulating support for the movable switch members of the three phases of the circuit.

The stationary and movable switch members for each phase are or may be identical and the construction of the switch members of but one phase will be described. The movable switch member of each phase comprises two vertically aligned contact members 28 and 30 which are carried by spring-urged frames 32 pivoted to a supporting bracket 34 fixed to the insulating bar 26. The contact members 28 and 30 are electrically connected through suitable means as the flexible conductor 36. Both movable contact members are electrically connected to a fixed terminal 38 by the flexible conductor 40.

Each phase of the switch has two fixed and relatively insulated contact members 42 and 44 which are disposed in vertical alignment and are supported by brackets 46 and 48 comprising circuit terminals of the switch carried by the insulating supporting plate 14. The contact members 42 and 44 are adapted to be connected in series in one phase of the multi-phase circuit controlled by the switch. The movable switch member is adapted to be connected electrically through. a resistance with one of the line contact members as the contact member 44. To this end, the

terminal 38 and the bracket 48 are provided H with cartridge-type fuse clips 50 and 52 respectively in which a cartridge-type resistance unit 54 inclosed within the insulating shell 56 and having the metal end caps or terminals 58 is removably received.

With this arrangement the contact members 28, 42, and 30, 44 are in series in the circuit and the resistor 54 is shunted around the contact members 30, 44. The resistor is thus in parallel with one of the circuit interrupting arcs and in series with the other circuit interrupting are.

This arrangement has been found to be effective in limiting the magnitude of the circuit' interrupting arcs and in promoting the extinguishment of the arcs so that the switch is able to handle a larger overload than when constructed in the ordinary manner. The resistor is removable so that one having a resistance suitable for use on any selected circuit can be installed in the switch.

Preferably the two sets of movable and stationary contact members are adapted to engage and separate simultaneously.

I claim:

1. An electric switch comprising sets of contact members each set comprising two contact members, the contact members of one set being insulated from each other and adapted to be connected in separate sections of a circuit, the contact members of the otherset being electrically connected, means efi'ecting the simultaneous separation of the sets of contact members, and means including a resistor connecting said electrically connected set of contact members to one of said electrically insulated contact members.

2. An electric switch having a pair of relatively insulated stationary contact members which are adapted to be connected in separate sect-ions of a circuit, a pair of electrically connected movable contact members which are adapted to engage and bridge said insulated members, means effecting the simultaneous separation of said pairs of contact members,

and means including a resistor connecting I said electrically connected movable contact members with one of said insulated contact members.

3. An electric switch having a pair of relatively insulated stationary contact members which are adapted to be connected in separate sections of a circuit, a pair of electrically connected movable contact members which are adapted to engage and bridge said insulated contact members, means eflecting the simultaneous separation of said pairs of contact members, and a resistor shunted about one of said movable and one of said fixed contact members and in series with the other two contact members.

4. An electric switch comprising a supporting plate, a pair of insulated line terminals having relatively insulated contact members carried by said fplate, a pivotally supported arm, a air 0 nected contact mem rs carried by said arm each cooperating with aseparate one of said fixed contact members, means efiectin simultaneous separation of said pairs 0 contact members, and a current limiting resistor electrically conthe connected. between said movable contact.

also simultaneously to disengage the coope'r ating set of stationary contact members, and resistors separately connected between each set of movable contact members and one of the contact members of each set of stationary contact members.

6. An electric switch having stationary switch members including a pair of relatively insulated fixed contact members, a movable switch member includin an insulating bar, a metal supporting brac et carried thereby, a pair of movable contact members pivotally mounted on said bracket and electrically connected with each other, operating mechanism for said movable switch member includin a p voted arm which carries said insulating bar, means eliecting the simultaneous separation of said pairs of contact members, and a resistor connected electrically with one of said fixed contact members, and having a flexible electrical connection with both of said movable contact members.

In testimony whereof, I have signed my name to this specification.

WILLIAM S. EDSALL. 

